A number of potentially important new synthetic routes to heterocyclic compounds and prostaglandins are outlined, all of which take advantage of the ease with which organopalladium compounds react with olefins or carbon monoxide to generate new carbon-carbon bonds. The immediate precursors of the organopalladium compounds are usually organomercurials and new routes to cis-vinylmercurials, acylmercurials, and a number of new functionally substituted organomercurials are proposed. The facile palladium-promoted ring-opening of cyclopropanes, cyclobutanes, epoxides, oxetanes, aziridines and Beta-lactones appears to afford new synthetic methodology applicable in the synthesis of pheromones, terpenes, and particularly nucleosides having antitumor, antimicrobial, and antiviral activity. Extensions of our newly developed, palladium-based heteroannulation approach to heterocycles are also proposed. These involve the synthesis of new reagents; the heteroannulation of simple alkenes, allylic halides, enones, siloxydienes and allenes; and extension of these reactions to simple organic halides. Potential applications in the synthesis of sesquiterpene lactones, vitamin E, and alkaloids possessing antitumor activity are outlined. The development of analogous carboannulation processes should prove valuable in the synthesis of carbocycles such as prostaglandins. New routes to unsaturated lactones, ethers, and carbocycles such as prostaglandins are also now available through intramolecular Pi-allylpalladium displacement processes. The intramolelcular cyclization of organopalladium compounds has been shown to provide new routes to butenolides and benzofurans, and these processes should prove applicable to the synthesis of lactams, coumarins, quinolones, isocoumarins, quinones, pyrones, indoles, oxindoles, isoquinolines, and the pyrrolizidine alkaloids. Finally, organopalladium additions to cyclic olefins and dienes have already provided highly efficient routes to prostaglandins of the A, E, and F series and many promising new routes to these and other prostaglandins have been uncovered. Successful completion of this work should 1) open up entirely new routes to many naturally occurring, biologically active heterocycles and prostaglandins; 2) provide a number of interesting new compounds which might show physiologicalactivity and hopefully medicinal utility; and finally 3) greatly shorten present syntheses of many vitally important heterocycles and prostaglandins.